SAN FRANCISCO -- Talk about hitting the ground running. Social networking site Facebook rolled out a new developer platform here, along with new applications created by more than 65 developer partners.

CEO and founder Mark Zuckerberg said the new Facebook Platform offers independent developers, for the first time, an opportunity to build full applications in a social networking site.

"We've constructed a framework that's completely optimized for building applications inside Facebook," said Zuckerberg. "We believe there is more value in having others build applications and develop completely new things."

It's a page right out of the playbook of Microsoft, which is legendary for its devotion to a vast network of third-party developers who build applications for the Windows platform. It's also akin to Google, which has been growing its own ecosystem of Web-based applications for the past few years. It also offers Google Apps for Your Domain, a free and paid suite of hosted applications such as calendar, e-mail, instant messaging, Google Docs and Spreadsheets.

But this approach has a social networking theme. At a press conference after the launch, Zuckerberg positioned Facebook's strategy as different than its biggest competitor, MySpace. "Our platform strategy isn't about owning all the content or owning all the applications," he said.

Zuckerberg described the three major components of the Platform as deep Integration into Facebook, mass Integration through the "social graph" that connects Facebook's users to each other, and new business opportunities for developers. Facebook said developers can create applications and keep all the ad or transaction revenue themselves.

Max Levchin, co-founder of PayPal and now CEO of photo sharing site Slide, compared Facebook's Platform strategy to Microsoft's longstanding (and wildly successful) support of third party developers for its operating system. "We're seeing a massively popular social Web site reborn as an operating system for a social computing platform," said Levchin.

"We genuinely believe it's possible to build popular applications on top of this OS (i.e. Facebook Platform)," said Levchin. "The opportunities are pretty massive." Slide applications, including Slide Shows for publishing and viewing personal photo slideshows; Slide SkinFlix for personalizing video clips with skins and themes; and the photo and video-sharing application Slide Guestbook can now be integrated Facebook user's profiles.

If Zuckerberg wasn't as explicit about the Microsoft comparison, he definitely is looking to the software giant as a model. "They are the master's of platform strategy and it only makes sense that we talk to each other," Zuckerberg told internetnews.com at the event. He said he talked to Microsoft's chief software architect Ray Ozzie last week and said the two companies are far more focused on working together than competing.

Executives from Amazon and Microsoft were on hand to voice their support for the Facebook Platform on stage. Microsoft already has a deal to provide Facebook with brand advertising and sponsored links. Now Facebook will support Microsoft's new Silverlight software, among other tools, for developing rich Internet applications.

"We're very supportive of this new opportunity," said Dan'l Lewin, Microsoft's corporate vice president for strategic and emerging business development. "Facebook may be the definitive opportunity on the Web for sharing data."

Russ Grandinetti, a vice president at Amazon, said the ecommerce giant is promoting its Web services platform to Facebook developers. Also, Amazon is making its Book Reviews application available to Facebook users which is designed to facilitate sharing of reviews, reader comments, and, of course, buy books.

The Platform launch comes at a time when Facebook is already experiencing explosive growth. The privately held company, based in Palo Alto, Calif., has over 24 million registered users worldwide and is the sixth most trafficked site in the U.S. according to Comscore's MediaMetrix report. As impressive as those numbers are, Facebook trails far behind MySpace, which has more than twice as many users.

Zuckerberg said the company is attracting a 100,000 more users a day and growing at a rate that could see it more than double in size in the next six months. Facebook had 15,000 users when it launched in 2004 as a social networking site for college students. In fact, it only opened up access to the general public last year. Zuckerberg said Facebook's fastest growing demographic now is adults 25 years and older.

"More than 50 percent of our users come back to our site every day," he said. "We don't know of any other [social network site] that has more than 15 percent return daily."